? Caterpillar identified as Yellow Coster

What’s this bug?
Can’t find anything like this by searching online, perhaps you can help. It was feeding on what appeared to be a giant stinging nettle, secreting what I guess is nettle venom from its thorny spines. Length: approx 2 1/4″

Hi Paul,
We originally thought this might be the caterpillar of the Question Mark, Polygonia interrogationis. But, the following letter just arrived.

(04/10/2007) Caterpillar Identifications
Hello WTB,
Having reared and photographed several hundred species of butterflies (no time for moths) for the past 25+ years, I thought you’d appreciate knowing two IDs that I noticed while quickly scanning your caterpillar pages last night . . .
? Caterpillar (04/27/2006) — “Yellow coster”, Acraea issoria (Nymphalidae, Heliconiinae, Acraeini); larval foodplant: many Urticaceae, e.g., non-stinging Boehmeria and Debregeasia in Taiwan and India. See pix of caterpillars and chrysalis at < http://nc.kl.edu.tw/bbs/showthread.php?t=7943 > (accompanying text in Chinese). I hope this information is helpful and of some interest. Best wishes,
Keith Wolfe
Antioch, CA

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